The present invention generally relates to a sealing apparatus for sealing the sealing face of an injection block and, in particular, relates to such apparatus having means for controlling the position of a sealing body with respect to the sealing face.
The seal of an injection block of a gas chromatograph is a critical factor in ensuring the accurate measurement of samples tested. There are two major considerations involved in attempting to properly seal such an injection block. The first major consideration is that the seal must be able to provide a quality seal even after a number of needle punctures. One problem associated with the repeated use of a particular seal beyond a relatively small number of punctures is that, during withdrawal of the needle, sample residue may remain in the sealing body and be carried into the next sample supplied and thus contaminate it. The second major consideration is that the exchanging or replacing of seals, particularly with automated sample injection apparatus, is usually a rather time consuming procedure.
One known approach to circumventing the problems discussed above is shown in U.S. Pat. No. 3,581,573 issued to Purchell et al. on June 1, 1971. The apparatus described therein comprises a sealing body having two distinct portions, a outer layer and an inner layer. Good sealing conditions are maintained by manually moving the inner layer, after it has been punctured, to present a fresh inner surface for the next puncture. While this apparatus is effective for providing a seal it nevertheless requires a two layered sealing body which is unnecessarily complicated. Another approach to the present problem is described in U.S. Pat. No. 3,646,093 issued to Downs et al. on Jan. 18, 1972. Therein a sealing member having, as an intergral part thereof a needle guide which is shifted from a seal position to a puncture position. When in the seal position the needle guide through the sealing body is covered by a solid portion of the movable member. This assembly has the drawback that the sealing body can still collect contaminents during probe withdrawal which can contaminate subsequent samples.